\documentclass{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}\textbf{S}_{k} = \textbf{H}\hat{\textbf{P}}_{k|k-1}\textbf{H}^{T} + \textbf{R}\end{equation*}
\end{document}
